Semiconductor memory devices may be classified as volatile and nonvolatile types, based on their ability to retain data therein without a power supply. Volatile memory devices may include static and dynamic random access memories, (i.e., SRAMs and DRAMs) while nonvolatile memory devices may include read-only memories (ROMs). ROMs may be of various types such as erasable and programmable ROMs (EPROMs), electrical EPROMs (EEPROMs), flash memories, and so on.
Nonvolatile memory devices may offer several advantages, as they may offer smaller sizes, lower power consumption, and/or advanced reading/writing performance. For example, flash memories may be used to provide on-chip memories for portable devices that may require relatively fast data updates, such as cellular phones, digital cameras, digital cameras, audio/video recorders, modems, smart cards, and so forth.
Some nonvolatile memory devices may need to be supplied with a voltage higher than a power source voltage, hereinafter, referred to as ‘high voltage’, for example, for writing operations by mechanisms of F-N tunneling, source-side channel hot electron injection, and so on. While the high voltage may be generated from the power source voltage, it may take time to generate the high voltage at a desired or target voltage level, also referred to herein as ‘setup time’. Once the high voltage reaches the target level, it may be applied to a selected memory cell (or selected memory cells) for a predetermined time, also referred to herein as ‘writing time’. A writing operation may include programming and erasing operations. After conducting a writing operation, the high voltage applied to a selected memory cell (or selected memory cells) may be discharged for a predetermined time, also referred to herein as ‘discharge time’. FIG. 1 illustrates waveform variation of a high voltage during a writing operation as described above. As shown in FIG. 1, the aforementioned procedure, including a setup time, a writing time, and a discharge time, may be repeated if successive writing operations are performed.
Accordingly, as the amount of data to be successively written into a memory device and/or the number of successive writing cycles increases, managing the writing time may become increasingly important.